1. Field of the Invention
This invention relates to a container suited to holding corrosive liquids and in particular to a container made from thermosetting resins. Containers of this type are frequently used in the construction of electrowinning cells used in the mining industry.
2. Description of Prior Art
U.S. Pat. Nos. 4.621,010 and 5,037,520 and Australian patent No. 659,400 describe typical prior art containers. These patents describe containers made using vinylester or polyester resins mixed with sand and gravel.
The container described in U.S. Pat. No. 5,037,520 is molded using a composition employing vinylester or polyester thermosetting resins. The addition of thinning agent, inhibitors, promoters and catalyst modify the resins. The balance of the composition includes dry ingredients of crystalline silica particles token from groups consisting of gloss beads and mica flakes. The resins are mixed with the dry ingredients and then the mixture is continuously poured into an inverted mold. They then allow the mixture to cure at room temperature providing a final container having a smooth inside, bottom side and end wall surfaces. This method results in a container having a wall thickness of about 2.5 inches or 62 mm.
U.S. Pat. No. 4,621,010 describes a laminated container where they employ a mixer designed to limit how much air is drawn into the mixture during the mixing process. Container integrity requires thorough mixing of the ingredients to coat the sand and gravel particles. This introduces air into the mixture promoting porosity in the container wall that can lead to cracks and leakage. It is therefore important to purge as much air as possible from the container wall. Porosity is still a problem despite the precautions taken in this method.
Australian patent No. 659,400 describes a laminated container using vibration to improve adhesion between a vinylester rich liner and a thick outer wall used to give strength and to support the liner. The liner serves the purpose of providing a high integrity non corrosive container while the vibration method reduces of delaminating over time.
Nevertheless all these containers suffer from disadvantages and there is room for improvement, in particular further reductions in air in the container wall is desirable as porosity is a problem that in even small amounts can lead to cracking over time. Another problem arises where the vibration method is in use to improve adhesion between the layers as there is a tendency for the sand in the outer layer to also abrade the wall of the mold in the same way. This makes it difficult to remove the container from the mold increasing labour costs and risking damage to the container or mold.